Integrated circuits (ICs) may include designs that contain sensitive information. An example of such sensitive information is the secret key information used in crypto engine implementations (such as AES). In security critical integrated circuits, security countermeasures are often implemented to provide safety of the sensitive information against side channel attacks. Some side channel attack techniques include physical attacks that require actual physical access to the inner layers of the integrated circuit. Passive or active shields can be added to ICs as countermeasures to protect sensitive information on ICs from unauthorized or unintended access methods for the circuit.
For both passive shielding and active shielding, an IC is covered with metal lines that are disposed on top of the IC, for example in the top metal layer to hide the circuit beneath. For active shielding, these metal lines are connected to a voltage supply (power and ground) or supplied with a predefined or random test data from a transmitter, and observed with a number of receivers located at certain points of the integrated circuit. For a case where the active shield uses a voltage supply, the receivers are also coupled to power or ground to compare whether there is a change. For a case using test data, the receivers may also be supplied with the same test data internally in order to compare the data on the shielding metals and the actual test data. The receivers verify the integrity of the metal lines based on the output of the comparison. However, detection of a breach may be avoided with attack techniques where a portion of the shield is cut and reconstructed with a technique such as a focused ion beam to create a potential attack zone.